Among the additives for hydraulic compositions, there is an agent called high performance water-reducing agent, which is highly effective in imparting fluidity. Representative examples thereof include naphthalenesulfonic acid-formaldehyde condensate salts (naphthalene-based), melaminesulfonic acid-formaldehyde condensate salts (melamine-based), polycarboxylic acids having a polyoxyalkylene chain, and the like.
In recent years, the tendency regarding concrete, which is a representative hydraulic composition, is more strongly oriented toward an increase in the durability, and for example, impartation of high strength is being achieved by reducing the amount of water used in concrete, while this tendency is anticipated to ever increase in the future. It has become prevalent to use polycarboxylic acid-based water-reducing agents having excellent water-reducing properties and fluidity maintainability in reducing the amount of water. However, this reduction in the amount of water is accompanied by an increase in the fresh concrete viscosity (hereinafter, may also be referred to as concrete viscosity), thus causing problems involving deterioration in the workability and constructibility such as in pressure pumping, stamping and filling into formwork. This problem of viscosity increment has not been satisfactorily addressed even with the polycarboxylic acid-based water-reducing agents, and an additive having a higher concrete viscosity-reducing effect is being desired.
Under such circumstances, JP-A 11-79811 discloses a concrete admixture containing, as an essential component, a vinyl copolymer having an oxyalkylene group with a long chain length and a specific monomer.
Meanwhile, JP-A 2000-327386 proposes to use a polymerization product of a monoester or monoether having a polyalkylene glycol chain with a monomer having an unsaturated bond and a phosphoric acid group, in order to obtain a dispersant for cement which can exhibit excellent fluidity properties, good dispersing effects and rapid setting properties, regardless of the mixing ratio of water.
As for the method for producing a cement dispersant by radical polymerization in the presence of a solvent, for example, JP-A 2001-146447 discloses a copolymer produced by reacting a polyalkylene glycol (meth)acrylate and/or polyalkylene glycol (meth) allyl ether with (meth) acrylic acid and/or maleic acid, using a polymerization solvent having a dissolved oxygen concentration of 0.01 to 4.0 mg/kg.
JP-A 2001-31722 discloses a method of copolymerizing an unsaturated polyalkylene glycol and an unsaturated polycarboxylic acid at a dissolved oxygen concentration of 5 ppm.
JP-A 2001-146450 discloses a method for producing a cement dispersant by subjecting a polyalkylene glycol-based monomer and a monomer containing a carboxylic acid-based monomer to a copolymerization reaction in the presence of a phosphonic acid-based chelating agent. In dispersants for hydraulic compositions, obtained by a copolymerization reaction, such as polycarboxylic acid dispersants, a molecular weight thereof may have a significant influence on the obtained performance of the copolymer, even with the same composition ratio (molar ratio). Although the adjustment of molecular weight on a laboratory scale can be controlled by varying the type or amount of the chain transfer agent, and the type or amount of the polymerization initiator, the process on an industrial scale is associated with many uncertainties, and the fluctuation in the molecular weight tends to increase.
Furthermore, in the production of polycarboxylic acid polymers, when a water-soluble thiol compound is used as a chain transfer agent, foul odor remains behind in many cases, which is likely to cause putrefaction during storage. Thus, complicated purification is needed to prevent these.
JP-A 1-226757 proposes a method which does not require the molecular weight adjustment using a water-soluble thiol compound, which process would otherwise necessitate complicated purification.
Furthermore, polymers obtained by a method of feeding monomers as shown in the method for producing polycarboxylic acid-based dispersants, exhibit significant variances in the performance required for a cement dispersant.
JP-A 1-226757 proposes a method of performing polymerization by introducing a monomer component and a chain transfer agent component into a reaction vessel in advance, and then adding a polymerization initiator.
JP-A 9-86990 proposes a method of performing polymerization while respectively adding dropwise a solution prepared in advance by mixing a monomer component and a chain transfer agent, and a polymerization initiator.
Conventional additives for hydraulic compositions often need to be stored in storage tanks until the time of use. If an organic substance like an additive for hydraulic compositions stagnates in the storage tank, anaerobic conditions gradually develop therein, and anaerobic bacteria grow in large quantities, causing contamination of the storage tank and generation of putrefying odor. Moreover, many of copolymers like the polycarboxylic acid-based water-reducing agents make use of a chain transfer agent in the reaction process. When a water-soluble thiol compound is used as a chain transfer agent, foul odor remains behind in many cases, which is likely to cause putrefaction during storage. Thus, complicated purification is needed to prevent these.
JP-A 2003-12357 proposes a degeneration preventive agent or a preventive agent for hydrogen sulfide generation.